Urlsnarf (as part of the dsniff package) is also available in entware. Alternatively you can setup a transparent proxy for logging, but I generally find urlsnarf less hassle.

Urlsnarf memory usage tends to creep up over time. For long term use, we have a cron job restart it every couple hours. Probably doesn't really need to be that often - once a day is likely more than enough.

We use entware, but have urlsnarf running 24/7 at several locations. No issues leaving it up. Our script is a little different than Shibby's primarily directing the output to syslog vs a file, otherwise very similar..

@jerm, good to know entware has the urlsnarf package. Typically I run entware versus optware on my router, but I switched back to optware to test something (I don't even remember why), plus I found Shibby's guide so it made things quick and simple.